The present invention relates to generally to printing plates, and more particularly, is directed to a single printing plate for printing both solid areas and highlight areas.
In known printing machines, such as flexographic printing machines, there are a number of printing stations in the printing press. Each inking station includes a printing plate mounted on a printing roller and an anilox roller for supplying ink to the printing plate on the printing roller. Each inking station prints with a different color ink. Accordingly, a web positioned between the impression cylinder of the inking station is printed with the image from the printing plate, with a different color ink at each inking station.
When printing on a web of material, there are solid color areas that are printed on the web as well as highlight color areas which are formed by spaced apart small dots. For example, for the diet cranberry-raspberry drink sold under the trademark “SNAPPLE”, there is a label on the bottle which includes solid dark purple areas as well as light purple areas. The solid dark purple areas are best printed generally by a first printing plate, and the light purple areas are highlights formed by spaced apart dots which are best printed by a second printing plate.
Each printing plate is mounted on a printing roller with a sticky back material, in effect, a material having adhesive on opposite sides, one for adhering to the printing roller and the other for adhering to the back of the printing plate.
It is known that the photopolymer printing plates for printing the solid colors have a lower durometer (softer) and a harder sticky back material, while the photopolymer printing plates for printing the highlights (dots) have a higher durometer (harder) and a softer sticky back material. It is also known to print the solid areas with more impression or a higher printing pressure, that is, the printing rollers are positioned closer to the impression cylinder to provide a greater force thereon, while the printing of the highlights occurs with less impression or a lesser printing pressure, that is, the printing rollers are positioned further away from the impression cylinder to provide a lesser force thereon. As a result, there is a higher ink transfer rate for the solid printed areas and a lower ink transfer rate for the highlight printed areas.
The problem with this arrangement is that it generally requires different printing plates, sticky back material and/or anilox roll for the solid areas versus highlight (dots) areas, and often, the durometer of the printing plate and the hardness of the sticky back material is changed in accordance with the required printing.